[Lydia, gautam]

To measure the modulation depth of the 29.5 MHz sideband, we plan to connect a bidirectional coupler between the EOM and the triple resonant circuit box. This will let us measure the power going into the EOM and the power in the reflection. According to the manual for the EOM (Newport 4064), the modulation depth is 13 mrad/V at a wavelength of 1000 nm. Before disconnecting these we will turn off the Marconi.

Hopefully we can be gentle enough that the EOM can be realigned without too much trouble. Before touching anything we'll measure the beam power before and after the EOM so we know what to match after.

If anyone has an objection to this plan, speak now or we will proceed tomorrow morning.

I'm afraid that the bidirectional coupler, designed to be 50ohm in/out, disturbs the resonant circuit designed for the EOM which is almost purely capacitive.

One possible way could be to measure the transfer function using the active FET probe from the triple resonant input to the output with the EOM attached.

Another way: How about to measure the reflection before the resonant circuit? Then, of course, there is the triple resonant interface circuit between the power combiner and the EOM. This case, we will see how much power is consumed in EOM and the resonant circuit. Then we can use the previous measurement to see the conversion factor between the power consumption to the modulation depth. Kiwamu may give us his measurement.

Just collecting some links from my elog searching today here for easy reference later.

• EOM datasheet: Newfocus 4064 (according to this, the input Impedance is 10pF, and can handle up to 10W max input RF power).
• An elog thread with some past measurement details: elog 5339. According to this, the modulation depth at 29.5 MHz is 4mrad. The EOM's manual says 13mrad/V @1000nm, so we expect an input signal at 29.5MHz of 0.3V(pk?). But presumably there is some dependance of this coefficient on the actual modulation frequency, which I could not find in the manual. Also, Kiwamu's note (see next bullet) says that the EOM was measured to have a modulation depth of 8 mrad/V
• A 2015 update from Kiwamu on the triple resonant circuit: elog 11109. In this elog, there is also a link to quite a detailed note that Kiwamu wrote, based on his analysis of how to make this circuit better. I will go through this, perhaps we want to pursue installing a better triple resonant circuit...

I couldn't find any details of the actual measurement technique, though perhaps I just didn't look for the right keywords. But Koji's suggestion of measuring powers with the bi-directional coupler before the triple resonant circuit (but after the power combiner) should be straightforward. 

The 3 pieces of Sapphire v-groove test cuts are back. They look good. The suspension wire 0.0017" ( 43 micron ) is show on some of the pictures.

Very nice! I got excited.

• Don't you ask Calum and co to check the groove size with their microscopes? Just give the samples and the wire.
• Do we want to make a simple "guitar" setup to measure the vibration Qs with Al piece, glass prism, ungrooved Sapphire, this grooved sapphire, grooved ruby, etc?

Rebooted c1iscaux, c1auxex and c1auxey which were all not reponding to telnet. The watchdogs for the ETMs were turned off and then I keyed all 3 crates. All slow machines are reponding to telnet now. Both green lasers locked to the arms so I didn't do any burt restore.

Just FYI I'm running a test of updated daqd code on fb1. 

fb1 has it's own fiber to the daq network switch, so nothing had to be modified to do this test. This *should* not affect anything in the rest of the system, but as we all know these are famous last words....  If something is going haywire, and you can't get in touch with me and can't figure what else to do, you can just log on to fb1 and shut it down.  It's not writing any data to any of the network filesystems.

The daqd code under test is from the latest advLigoRTS 3.2.1 tag, which has daqd stability fixes that will hopefully address the problems we were seeing last time I tried this upgrade.  We'll see...

I'm going to let it run over the weekend, and will check in periodically.

I'm not sure if this is related, but since today morning, I've noticed that the data concentrator errors have returned. Looking at daqd.log, there is a 1 second timing mismatch error that is being generated. Usually, manually running ntpdate on the front ends fixes this problem, but it did not work today.

The coil and PD BLRMS are useful tools in identifying when glitches occur in the PD  readout, I thought it would be good to install them for ITMY, ETMX and SRM (since I plan to switch the MC3 satellite box, which we suspect to be problematic, with the SRM one). For this purpose, I had to install some IPC SHMEM blocks in C1SUS and recompile. 24 IPC channels were added to pipe the coil, PD and Oplev signals from C1SUS to C1PEM - the recompilation went smoothly, and it doesn't look like the model computation time has increased significantly or that the model is any closer to timing out.

However, I was unable to install the BLRMS blocks in C1PEM, as when I tried to compile the model with BLRMS for these extra 24 channels, I got a compilation error saying that I have exceeded the maximum allowed 499 testpoints per channel. Is there any workaround to this? It would be possible to create a custom BLRMS block that doesn't have all those testpoints, maybe this is the way to go? Especially if we want to install these channels for all our SOS optics, and also replace the current Seismic BLRMS with this scheme for consistency?

GV edit: I have implemented this scheme - after backing up the original BLRMS_2k part, I made a new one with no testpoints and only EPICS readouts. Doing so allowed me to recompile c1pem without any issues, the CPU time seems to have gone up by 3us from ~55us to 58us. So the BLRMS data record is only available at 16Hz, since there are no DQ channels in the BRLMS block - do we want these in any case? Let's see how this does over the weekend...

[gautam, Lydia]

We set out to measure the 29.5 MHz power going to the EOM today but decided to start by looking at the output of the RF AM stabilizer box first. We wanted to measure the AM noise with a mixer, so we needed to know the power it was giving. We looked at the ouput that goes to the power combiner on the PSL table and found it was putting out only -2.0 dBm (~0.5 Vpp)! This was measured by taking a spectrum with the AG4395 and confirmed by looking on a scope.

To find out if this could be adjusted, we found an old MEDM screen (/opt/rtcds/caltech/c1/medm/c1lsc/master/C1LSC_RFADJUST.adl) and moved the 29.5 MHz EOM Mod Index Adjust slider while measuring the voltage coming in to the MOD CONTOL connection on the front of the AM stabilizer box. Moving the slider from 0 to 10 changes the input voltage linearly from -10 V to 10 V measured with a DMM at the cross-connects as we couldn't find an appropriate adapter for the LEMO cable. The 29.5 MHz modulation only appeared for slider values between 0 and 5, after which it abruptly shuts off. However, changing the slider value between 0 and 5 (Voltage from -10 to 0) does not change the amplitude of the output.

This seems like a problem; further investigation into the AM stabilizer box is neccessary. This DCC document outlines how to test the box, but we can't find a schematic. Since we don't have any mixers that can handle signals as small as -2 dBm, we gave up trying to measure the AM noise and will attempt to measure that and the reflection power from the EOM + resonant circuit once this problem has been diagnosed and fixed.

GV: After some digging, I found the schematic for the RF AM stabilization box (updated wiki and added it to the 40m document tree). According to it, there should be up to +22dBm of RF AM stabilized output to the EOM available, though we measured -2dBm yesterday, and could not vary this level by adjusting the EPICS voltage value. Neglecting losses in the cabling and the power combiner on the PSL, this translates to a paltry 0.178Vrms*0.6*8mard/Vrms ~ 0.85 mrad of modulation depth (gain at 29.5 MHz of the triple resonant circuit taken from this elog)... I think we need to pull this 1U chassis out and debug more thoroughly...

Some more details of our investigation:

1. Here is a spectrum of the signal to the power combiner on the PSL table, measured on the output of the RF AM Stabilization box.
   
   Perhaps these sidebands were the ones I observed while looking at the input to the WFS demod board.
2. The signal looked like a clean sinusoid when viewed on an oscilloscope with input impedance set to 50ohms. There were no sharp features or glitches in the time we observed, except when the 29.5 MHz MEDM slider was increased beyond 5, as noted by Lydia.
3. We couldn't find a schematic for this RF AM Stabilization servo, so we are not sure what RF output power to the EOM we should expect. Schematic has since been found.
4. I measured the power level at the input side (i.e. from the crystal) and found that it is ~12dBm, which seems reasonable (the front panel of the box housing the 29.5 MHz oscillator is labelled 13dBm). The schematic for the RF AM stabilization box says we should expect +10dBm at the input side, so all this points to a problem in the RF AM stabilization circuit...
5. There is an attenuator dial on the front panel of the said RF AM stabilization servo that allows one to tune the power to the LO input of the WFS. Right now, it is set to approximately 7dB of attentuation, which corresponds to -12dBm at the WFS demod board input. I did a quick check to see if turning the dial changed the signal level at the LO input of the WFS board. The dial moves in clicks of 1dB, and the RF power at the LO input of the demod board increased/decreased by ~1dBm for each click the dial was rotated (I only explored the region 3dB-11dB of atttentuation). So it should be possible to increase the LO level to the WFS demod boards, is there any reason we shouldn't increase this to -8bBm (~0.25Vpp into 50ohms, which is around the level Koji verified the mixer to be working well at)?
6. There were a couple of short ribbon cables which were just lying around on top of the cards in the eurocrate, Koji tells me that these were used as tester cables for checking the whitening filters and that they don't serve any purpose now. These have been removed.
7. Added a button to IMC MEDM screen to allow easy access to the MEDM screen with slider to control the 29.5MHz modulation depth - though as mentioned in Lydia's elog, at the moment, this slider has no effect on the 29.5MHz power level to the EOM...
   

If this problem started before ~4pm on Friday then it's probably unrelated, since I didn't start any of these tests until after that.  If unexplained problem persist then we can try shutting of the fb1 daqd and see if that helps.

I just aborted the fb1 test and reverted everything to the nominal configuration.  Everything looks to be operating nominally.  Front ends are mostly green except for c1rfm and c1asx which are currently not being acquired by the DAQ, and an unknown IPC error with c1daf.  Please let me know if any unusual problems are encountered.

The behavior of daqd on fb1 with the latest release (3.2.1) was not improved.  After turning on the full pipe it was back to crashing every 10 minutes or so when the full and second trend frames were being written out.  lame.  back to the drawing board...

[johannes, gautam]

We pulled out the RF AM stabilization box from the 1X2 rack. PSL shutter was closed, marconi output, RF distribution box and RF AM stabilization box were turned off in that order. We had to remove the 4 rack nut screws on the RF distribution box because of the stiff cables which prevented the RF AM stabilization box extraction. I've left the marconi output and the RF distribution boxes off, and have terminated all open SMA connections with 50 ohm terminators just in case. Rack nuts for RF distribution box have been removed, it is currently sitting on a metal plate that is itself screwed onto the rack. I deemed this a stable enough ledge for the box to sit on in the short run, while we debug the RF AM stabilization box. We will work on the debugging and re-install the box as soon as we are done...

[gautam, Lydia]

We looked at the RF AM stabilizer box to see if we could find out 1) Why the output power is so low, and 2) Why it can't be changed with the DC input "MOD CONT IN." Details to follow, attached is the annotated schematic from DCC document D000037. 

We are not returning the box tonight so the PSL shutter remains closed. 

1. What is the probe situation? Ought to use a high impedance FET probe to measure this or else the scope would load the circuit.
2. The ERA amplifiers are known to slowly die over ~10 year times scales. Search our ELOG for ERA-5. We'll have to replace some; ask Steve to order if we don't have many in the Plateau Tournant.
3. What kind of HELA are the HELA amplifiers? Please a link to the data sheet if you can find it. I wonder what the gain and NF are at 30 MHz. I think the HELA-10D should be a good variant.

I think this cron job is running on NODUS (our gateway) instead of our scripts machine:

*/1 * * * * /opt/rtcds/caltech/c1/scripts/Admin/n2Check.sh >> /opt/rtcds/caltech/c1/scripts/Admin/n2Check.log 2>&1

moreover this script has a 90MB log file full of not finding its channel

I wish this script was in python instead of BASH and I wish it would run on megatron instead of nodus (why can't megatron send us email too?) and I wish that this log file would get wiped out once in awhile. Currently its been spitting out errors since at least a month ago:

Tue Jan 31 14:10:02 PST 2017 : N2 Pressure:

Channel connect timed out: 'C1:Vac-N2pres' not found.

(standard_in) 1: syntax error

> What is the probe situation? Ought to use a high impedance FET probe to measure this or else the scope would load the circuit.

We did indeed use the active probe, with the 100:1 attenuator in place. The values Lydia has quoted have 40dB added to account for this.

> What kind of HELA are the HELA amplifiers? Please a link to the data sheet if you can find it. I wonder what the gain and NF are at 30 MHz. I think the HELA-10D should be a good variant

The HELA is marked as HELA-10. It doesn't have the '+' suffix but according to the datasheet, it seems like it is just not RoHS compliant. It isn't indicated which of the varieties (A-D) is used either on the schematic or the IC, only B and D are 50ohms. For all of them, the typical gain is 11-12dB, and NF of 3.5dB.

I've been suggesting that there may be something wonky with the Seismic Rainbow Striptool on the wall for the last couple of weeks. Here are a few things that were verified today.

1. If you want to restore the StripTools in the control room, just run /opt/rtcds/caltech/c1/scripts/general/startStrip.sh. I have verified as of today that this works, and in future, any changes to channels/limits/colors of traces etc should be reflected in this script.
2. Though some of the BLRMS bands have looked anomalous over the last few weeks, in particular the 0.3-1Hz band. The attached 120 day trend plot suggests that there hasn't been any dramatic change recently. In fact, looking on the summary pages, Rana noticed that today was an unusually low 0.3-1Hz activity day..

I've added the schematic of the RF AM stabilization board to the 40m PSL document tree, after having created a new DCC document for our 40m edits. Pictures of the board before and after modification will also be uploaded here...

I made a crude sketch for how Lydia and I envision the connector situation on the back of the vme crates to be solved. Essentially the side panels of each crate extend about 2" (52 mm) beyond the edge of the DIN connectors. This is plenty of space for a simple PCB board. The connector of choice is D-Sub. We can split the 64 used pins into 2x 37 D-Sub OR (2x25 pin + 1x15pin). The former has fewer cables, but a few excess unused leads. A quick google search showed me that it is much cheaper to get twisted pair cables for 15 and 25 pin D-Subs. From what I remember, the used pins on the DIN connectors are concentrated on the low numbers end and the high numbers end, so might not need the 'middle' connector in many cases if we decide to break it up into three. I have to check this with Lydia though.

The D-Sub connectors would be panel mounted, for which we need a narrow panel piece with dsub cutouts. We can run horizontal struts across the vme crate from side panel to side panel. This way the force upon cable (dis)connection is mostly on the panel which is attached to the struts which are attached to the crate. This will also prevent gravitational sag or cable strain from pulling on the DIN connection, and we can use twisted pair cables with backshell, screws, and strain reliefs.

I was lookng into getting started with the PCB when Altium complained that the license is expired and to renew it. This is a relatively simple board layout so some free software out there is probably enough.

[rana, gautam, lydia]

Today we looked at the schematics for the RF AM stabilizer box and decided that there were an unnecessary amount of attenuators and amplifiers cancelling each other out and adding noise. At the end of the path are 2 HELA-10D amplifiers which we guessed based on the plots for the B version would have an acceptable amount of compression if the output of the second one is ~27dBm. This means the input to the first one should be a few dBm. This should be achieved with as simple a path as possible.

This begged the question, do we need the amplitude to be stabilized at all? Maybe it's good enough already when it comes into this box from the RF distribution box. So I tried to measure the AM noise of the 29.5 MHz signal that usually goes into the AM stabilizer:

• I first measured the power to be 12.8 dBm with the AG4395.
• I sent the signal through a splitter, then sent one side attenuated by 3 dB to the LO side of a level 7 mixer, and the other side attenuated by 10 dB to the RF side of the mixer.
• The output of the mixer went through a lowpass filter at 1.9 MHz (with a 50Ω inline terminator). Initially I connected this directly to a DAQ channel (C1:ALS-FC_X_F_IN), but the ADC noise was stronger than the AM signal.
• To fix this I used the SR560, AC coupled with a gain of 10^4. Attachment 1 is a spectrum of the noise measured with everything connected as described, and also for separate portions of the signal chain:
  • I measured the ADC noise by connecting a terminator to the cable going to DAQ.
  • I measured the mixer noise by putting a terminator on the RF input (and the end of the cable that was connected to it), while still driving LO.
  • I measured the SR560 noise by putting a terminator on the input.

It seems like I'm getting mostly noise from the SR560. Maybe it would be better to use an SR785 to take data instead of DAQ, and then skip the SR560? At low frequencies it seems like the AM noise measurement may be actually meaningful. In any case, if the actual AM noise from the crystal is lower than any of these other noise sources, it means we probably don't need to stabilize the amplitude with a servo, which means we can simplify the AM stabilizer board considerably to just amplify what it gets to 27 dBm.

For a comparison: OMC ELOG 238

Here's what I'm planning to do to the RF AM stabilizer box. I'm going to take out several of the components along the path to the EOM (comments in green), including the dead ERA-4 and ERA-5 amplifiers, the variable attenuator which is controlled by a switch that can't be accessed outside the box, and the feedback path from the daughter board servo. I'm arranging things so that the output of the HELA-10 does not exceed the maximum output power. 

I wasn't quite as sure what to do about the path to the ASC box (comments in blue). I talked with Gautam and he said this gets split equally between several singals, one of which goes to the LO of the demod board which expects -10 dBm and currently gets -12 dBm (can go up to -8 by turning switch). So maybe we don't actually want the signal to be anywhere near +27 dBm at the output. The plans for the box are here, it looks like +27 in will end up with +10 at each output, which is way more than what's currently coming out. But maybe this needs to be increased to match the other path? 

Also we haven't measured the actual response of the variable attenuator U4 for various switch positions; it's the same model as the one I'm removing from the EOM path and that one had slightly different behavior for different switch positions than what the spec sheet says. Same goes for the HELA-10 units along this path: what is their actual gain? So perhaps these should be measured and then a single attenuator should be chosen to get the right output signal level. Alternatively it could just be left alone, if it is at an OK level right now. Advice on what to do here would be appreciated.  

I'll work on the EOM path tonight and wait for feedback on the rest of it. 

EDIT: Gautam pointed out that there's some insertion loss from the components I'll be removing that hasn't been accounted for. Also the plans have been updated to reflect that I'm replacing AT5 with a 1dB attenuator (from 6 dB). 

I suggest:

1. Disable the path which goes to the two spare outputs. Replace the ERA-5 with a 50 Ohm resistor to terminate that path. Make sure the ERA bias voltage is not shorting into something.
2. Remove the ERA amps from the ASC path and remove the switch. Make it fixed gain such that we get +27 dBm out of the front.
3. Put the ASC output into the 1U multi-splitter box and attenuate those outputs so that they supply ~0 dBm to the 2 WFS and the LSC Demod board.

I think this then allows us to have the low noise OCXO signals everywhere with enough oomph.

I made some of the changes. Gautam and I will finish tomorrow. 

While I was soldering the sharpest tip of the soldering iron (the one whose power supply shows the temperature) stopped working and I switched to a different one. Not sure how to fix this. 

Do we want to replace all of the removed ERA's with 50 Ohm resistors, or just the one along the spare output path? I shorted one of them with a piece of wire and left all the others open. 

I couldn't get one of the attenuators off (AT1, at beginning of ASC path). In trying I messed up the solder pad. Part of the connecting trace on the PCB board is exposed so we should be able to fix it. 

FYI this issue has still not been solved, but the pages are working because I got the software running on an
alternative headnode (pcdev2). This may cause unexpected behavior (or not).

> LDAS has not recovered from maintenance causing the pages to remain unavailable until further notice.
> 
> > System-wide CIT LDAS cluster maintenance may cause disruptions to summary pages today. 

This AmScope microscope would have 3.5x-180x magnification, calibratable measurement function, 5MP picture and good working distance to work on printed circuit boards.

I don't know if anyone looked at the time series (not trend) or spectrum of the Microphone after installation, but it looks bad and featureless to me. Is the Microphone broken?

This shows the spectrum from early this morning and again from tonight. You can see that it is bi-stable in its noise properties. This thing is busted; we're now removing it from the PSL so that it doesn' light it self on fire.

I had noticed something wonky with the microphone, but neglected to elog it. I had tested it after installation by playing a sine wave from my laptop and looking at the signal on the PSL table, it worked fine. But you can see in the attached minute trend plot that the signal characteristics changed abruptly ~half a day after installation, and never quite recovered.\

Rana motivated me to take a step back and reframe the objectives and approach for this project, so I am collecting some thoughts here on my understanding of it. As I write this, some things still remain unclear to me, so I am leaving these as questions here for me to think about...

Objectives: 

1. The PSL is locked to the IMC cavity - but at frequencies near 1 Hz, the laser frequency is forced to follow the IMC cavity length fluctuations, even though the free-running PSL frequency noise at those frequencies is lower. This excess is also imprinted on the arms when locked to the IR. We would like to improve the situation by feeding back a portion of the MC PDH error signal to the cavity length actuator to stabilize the MC cavity length at low frequencies. Moreover, we would like this loop to not imprint additional control noise in the arm control signals, which is a problem we have observed with the existing MCL loop. 
    
2. The borader goal here is to use this project as a case study for designing the optimal loop and adaptive feedback. Can we come up with an algorithm, which takes
   • A model of our system (made with measured data where possible)
   • A list of our requirements (e.g. in this case, frequency noise requirements in various frequency bands, smooth crossovers between the various loops that enable locking the PSL to the IMC cavity and avoid injecting excess control noise into the plant)

and come up with the best loop that meets all our rquirements? What constitutes the "best" loop? How do we weight the relative importance of our various requirements? 

Proposed approach:

For the specific problem of making the MCL feedback loop better, the approach I have in mind right now is the following:

1. Build a model of the 40m IMC loop. Ultimately the performance of the loop we implement will depend on the transfer function from various additive noise sources and disturbances in the feedback loop (e.g. electronics noise) to the output (i.e. laser frequency). Building an accurate model will allow us to quantify the performance of the proposed control loop, and hence, optimize it with some algorithm. I did some work on a simplistic, purely analytical model of the two MC loops (MCF and MCL), but Rana pointed out that it is better to have something more realistic for this purpose. I have inherited his Simulink models, which I will now adapt to reflect the 40m topology. 
2. Come up with a list of requirements for the MCL controller. Some things that come to mind:
   • Reduce the arm control signal spectral amplitude below 20 Hz
   • Not increase the arm control signal spectral amplitude above 20 Hz
   • Crossover smoothly with the FSS slow temperature control loop and the MCF loop. 
   • What factor of suppression are we looking for? What is achievable? Once I build the model, it should shed some light on these..
   • Is the PMC a more stable frequency reference than the NPRO crystal at low frequencies? This measurement by Koji seems to suggest that it isn't (assuming the 1e4 product for the NPRO free-running frequency noise)..
3. Once we have a model and a satisfactory list of requirements, design a control loop that meets these using traditional techniques, i.e. desired tracking error in the control band of 0.1-20 Hz (is this possible? The model will tell us...), gain and phase margin requirements etc. But this need not necessarily be the optimal controller that meets all of our requirements
4. Optimize the controller - how? Can we define an objective function that, for example, rewards arm control signal suppression and penalizes injection of control noise, and just fminsearch in the [z,p,k] parameter space of the controller? Is there a smarter way to do this?
5. Can this algorithm be adaptive, and optimize the controller to adapt to prevailing seismic conditions for example? Is this the same as saying we have a model that is accurate enough for us to predict the response of the plant to environmental disturbances? 

My immediate goal is to have the Simulink model updated.

Thoughts/comments on the above will be appreciated...

More testing of fb1 today.  DAQ DOWN UNTIL FURTHER NOTICE.

Testing Wednesday did not resolve anything, but Jonathan Hanks is helping.

In working on automatic DARM loop design, we have this code:

https://git.ligo.org/rana-adhikari/ModernControls/tree/master/OptimalFeedback/GlobalCost

the things in there like mkCost*, etc. have examples of the cost functions that are used. It may be useful to look at those and then make a similar cost function calculation for the MCL/MCF loop.

Since the "stablizer box" doesn't really need to stabilize, it just needs to amplify, I decided to replace it with an off the shelf amplifier we already had, ZHL-2. I worked on getting it set up today, but didn't connect anything so that people have a chance to give some feedback. 

• The gain we expect is 18 dB, and the maximum output with 1dB of compression is 29 dBm. To avoid compression, I'm aiming for ~26 dBm output, so ~8 dBm input. We measured the output of the source to be 12.8 dBm before, so I attached a 5dB attenuator to the input side of the amplifier. 
• Across the 24V power input and the ground pin, I soldered a 100 uF, 50V electrolytic capacitor and a .27 uF, 50V metal film capacitor. Note that unlike the other similar amplifiers we have, the ground and +24 pins are separated (see image on datasheet). I wasn't sure if that changed what to do so I just found comparable caps to the ones that were there on another model. 
• I twisted and soldered wires to the +24 and ground, making sure they were long enough to reach the clips where the power from the Sorensens gets split up. I placed the amplifer in the rack on top of the RF distribution box and ziptied the power cable in place. 
• I connected a splitter to the output of the amplifier. Should I use a 10dB coupler instead, to maximize the power to the EOM?

So, I think the remaining thing to do is to connect the splitter to ASC out and to the line to the EOM, the +24V supply to the amplifier, and the 29.5 MHz input to the attenuator. I wanted to wait on this to get confiration that the setup is OK. Eventually we can put all of this in a box. 

Also, I noticed that in the clear cabinet with the Sorensens next to this rack, the +24 V unit is not supplying any voltage and has a red light that says "OVP." 

The bottom 5 cable connections from Sat-Amp to Whittering Filter at 1X5 were clamped today.

Had to reboot c1psl, c1susaux, c1auxex, c1auxey and c1iscaux today. PMC has been relocked. ITMX didn't get stuck. According to this thread, there have been two instances in the last 10 days in which c1psl and c1susaux have failed. Since we seem to be doing this often lately, I've made a little script that uses the netcat utility to check which slow machines respond to telnet, it is located at /opt/rtcds/caltech/c1/scripts/cds/testSlowMachines.bash.

The script can be executed by ./testSlowMachines.bash.

I've edited Rana's Simulink model to reflect the current IMC servo topology (to the best of my understanding). I've tried to use Transfer Function blocks wherever possible so that we can just put in the appropriate zpk model in the script that will linearize the whole loop. I've also omitted the FSS SLOW loop for now.

I've been looking through some old elogs and it looks like there have been several modifications to both the MC servo board (D040180) and the TT FSS Box (D040105). I think it is easiest just to measure these TFs since the IMC is still down, so I will set about doing that today. There is also a Pomona Box between the broadband EOM and the output of the TT FSS box, which is meant to sum in the modulation for PMC locking, about which I have not yet found anything on the elog.

So the next steps are:

1. Measure/estimate all the unknown TFs and gains in this schematic
2. Linearize the model, get the OLG, see if the model matches previously measured OLGs (with the MCL part disabled)
3. Once the model is verified to be correct, look at couplings of various noise sources in the MCL part of the loop, and come up with a suitable controller.

If anyone sees something wrong with this topology, please let me know so that I can make the required changes.

It is more accurate to model the physical frequency noises at various places.

cf. See also 40m ALS paper or Shigeo Nagano PDH thesis on https://wiki-40m.ligo.caltech.edu/40m_Library

- The output 4 should be "Laser frequency"

- Seismic path should be excluded from the summing node

- The output after the PMC: "Laser frequency after the PMC"

- "Laser frequency after the PMC" is compared (diffed) with the output 1 "mirror motion in Hz"

- The comparator output goes to the cav pole, the PD, and the PDH gain: This is the output named "PDH Error"

- Tap a new path from "Laser frequency after the PMC" and multiply with the cav pole (C_IMC)
- Tap a new path from "Mirror motion" and multiply with the cavity high pass  (s C_IMC/omega)
- Add these two: This is the output named "Frequency noise transmitted by IMC"

A few minutes back, I glanced up at the control room StripTool and noticed that the MCREFL PD DC level had gone up from ~0 to ~0.7, even though the PSL shutter was closed. This seemed bizzare to me. Strangely, simply cycling the shutter returned the value to the expected value of 0. I wonder if this is just a CDS problem to do with c1iool0 or c1psl? (both seem to be responding to telnet though...)

Since things look to be back to normal, I am going to start with my characterization of the various TFs in the IMC FSS loop...

I tested the amplifier with the Agilent network analyzer and measured 19.5 dB of gain between 29 and 30 mHz. The phase only changed by 1 degree over this same 1 MHz span. Since everything seems to be in order I'll hook it up this afternoon, unless there are any objections. 

                                                                                                                                   received this note: at 4:11pm Tuesday, Feb 7, 2017

**PLEASE POST**

Building:         Campus

Date:             Wednesday, February 8, 2017

Time:             7:30 AM – 8:30 AM  

Contact:          Rick Rodriguez x-2576

Pasadena Water and Power (PWP) will be performing a switching operation of the

Caltech Electrical Distribution System that is expected to be transparent to Caltech,

but could result in a minor power anomaly that might affect very sensitive equipment.

IMPACT: Negligible impact......?

There may be temporary  power interruption tomorrow!

PS:we did not see any effect   

I set everything up and connected it as shown on the block diagram attached to the previous entry, with the exception of the DC power. This is becuase there is no place open to connect to on the DIN rail where the DC power is distributed, so the +24V power will have to be shut off to the other equipment in 1X1 before we can connect the amplifier. (The amplifier is in 1X2, but the DC power distribution was more accessible in 1X1.) I also added 3 new +24 V clips with fuses despite needing only one, so next time we need to connect something new it's not such a hassle. 

The RF distribution box where the 29.5 MHz signal originates should not be turned on until the amplifer has DC power. Since we may have a power interruption tomorrow, the plan is to wait until things are shut down in preparation, and then shut off anyhting else necessary before connecting the new clips on the rail to the existing ones. 

After fighting with Altium for what seems like an eternity I have finished putting my vision of the vme crate backplane adapter board into an electronic format. It is dimensioned to fill the back space of the crate exactly. The connectors are panel mount and the PCB attaches to the connectors with screws, such that the whole thing will be mechanically much more stable than the current configuration. A mounting bracket will attach to horizontal struts that need to be installed in the crates, mechanical drawings to follow.

The ITMX oplev beam is clipping. It will be corected with locked arm

Quick summary elog, details to follow. I did the following:

• Updated the Simulink model based on Koji's feedback. 
• Today morning, I measured the (electronic) open-loop TFs of
  • MC Servo Board
  • FSS Fast path (PZT)
  • FSS PC Drive path
• The summing amplifiers in the latter two paths are assumed to be broadband for the purposes of this model.

The measurements I have look reasonable. But I had a hard time trying to look at the schematic and determine what is the appropriate number and locations of poles/zeros with which to fit the measured transfer function. Koji and I spent some time trying to go through the MC Servo board schematic, but looks like the version uploaded on the 40m DCC tree doesn't have changes made to it reflected (we compared to pictures on the 40m google photos page and saw a number of component values were different). Since the deviation between fit and measurement only occurs above 1MHz (while using poles/zeros inferred from the schematic), we decided against pulling out the servo board and investigating further - but this should be done at the next opportunity. I've marked the changes we caught on a schematic and will upload it to the 40m DCC page, and we can update this when we get the chance.

So it remains to fit the other two measured TFs, and add them to the Simulink model. Then the only unknown will be the PDH discriminant, which we anyway want to characterize given that we will soon have much more modulation.  

Data + plots + fits + updated schematics to follow...

http://www.amscope.com/3-5x-180x-boom-stand-trinocular-zoom-stereo-microscope-with-144-led-ring-light-and-10mp-camera.html will be ordered today.

The actual unit we are getting has lockable zoom for better repeatability after calibration: SM-3NTPZZ-144

Quote: CWQ6-020817

I'd like to fix a few things at 1X1 when we plug in the new amplifier for the 29.5MHz modulation signal. 

1. Split off separate +24 and ground wires to the green BBPD RF amplifiers and the AOM driver (they are sharing a single fuse at the moment)
2. Tap a new +24 GND -24V set for the FSS Fast summing box - this is currently running with a bench power supply underneath the PSL table set to +/-18V, but I checked the 7815/7915 datasheets and they accept up to 35V input for a 15V output, so it should be fine to use 24V
3. Hook up the ZHL-2A for the IMC modulation.

Steve has ordered rolls of pre-twisted wire to run from 1X1 to the PSL table, so that part can be handled later.

But at 1X1, we need to tap new paths from +/- 24V to the DIN connectors. I think it's probably fine to turn off the two Sorensens, do the wiring, and then turn them back on, but is there any procedure for how this should be done? 

Here are the details as promised.

Attachment #1: Updated simulink model. Since I haven't actually run this model, all the TF blocks are annotated "???", but I will post an updated version once I have run the model (and fix some of the questionable aesthetic choices)

Attachment #2: Measured and fitted transfer functions from the "IN1" input (where the demodulated MC REFL goes) to the "SERVO" output of the MC servo board (to FSS box). As mentioned in my previous elog, I had to put in a pole (fitted to be at ~2MHz, called pole 9 in the plot) in order to get good agreement between fit an measurement up to 10MHz. I didn't bother fitting all the high frequency features. Both gain sliders on the MEDM screen ("IN1 Gain" and "VCO gain") were set to 0dB for this measurement, while the super boosts were all OFF.

Attachment #3: Measured and fitted transfer function from "TEST 1 IN" to "FAST OUT" of the FSS box. Both gains on the FSS MEDM screen ("Common gain adjust" and "fast gain adjust") were set to 0dB for this measurement. I didn't need any ad-hoc poles and zeros for this fit (i.e. I can map all the fitted poles and zeros to the schematic), but the fit starts to deviate from the measurement just below 1 MHz.. perhaps I need to add a zero above 1MHz, but I can't see why from the schematic...

Attachment #4: Measured TF from "TEST 1 IN" to "PC OUT" on the FSS box. MEDM gains were once again 0dB. I can't get a good fit to this, mainly because I can't decipher the poles and zeros for this path from the schematic (there are actually deviations from the schematic posted on the 40m DCC page in terms of component values, I will try and correct whatever I notice) . I'll work on this...

Attachment #5: Data files + .fil files used to fit the data with LISO

Most of the model has come together, I am not too far from matching the modelled OLG to the measured OLG. So I will now start thinking about designing the controller for the MCL part (there are a couple of TFs that have to be measured for this path).

Lydia finished up installing the new RF amplifier, and will elog the details of the installation.

I wanted to try and measure the IMC OLG to compare against my Simulink model. So I went about performing a few checks. Summary of my findings:

1. The amplifier seems to be working fine. I checked powers at the input, output to EOM and output to distribution box (that serves the various LOs) first with a 30dB attenuator at the input, and subsequently with the design choice of 5dB attenuator at the input. Everything seemed in order.
2. I installed a 30 dB attenuator at the MC REFL PD input to the demod board since my (rough) calculations suggested that our modifications would have resulted in the RF beat power between carrier and sideband increasing in power by ~27dB.
3. I then opened the PSL shutter and tried locking the IMC - with manual tweaking of the various gains, I was able to lock.
4. But getting to this point took me a while so I couldn't get an OLG measurement in.

TBC tomorrow, I'm leaving the PSL shutter closed and the RF source off for tonight...

To install the replacement amplifier, I did the following:

• Mounted the amplifier in a 2U chassis, with a metal plate between the amplifier and the bottom of the box. The plate is separated from the box and the amplifier with 2 sets of Nylon screws. I did it this way to make use of the holes that were already in the chassis bottom and just drill holes into a plate instead. 
• Cannibalized mounting brackets and back panel from old ALS Beatbox. The back panel has an on/off switch and a 3W3 feedthrough for power. 
• Made a power cable to reach from the 1X1 fuse blocks to the back panel of my box. Goes up through the top of the rack and then back down. 
• Installed the chassis in the rack. The lid is currently off and there is no front panel yet. 
• Changed the +5dB attenuator to +30 to be able to check things first before supplying a way stronger signal. 
• Installed 4 new +24 V fuse blocks on the adjacent rack (1X1). 
  • Put the new fuses on the DIN rail and wired them together. Connected the new power cable to one of them. 
  • Blocked PMC transmission and made sure all RF sources in 1X1 and 1X2 were turned off
  • Turned off the + 24 V and -24 V Sorensens, trying to keep them fairly balanced as I turned them to 0. 
  • At this point Rana suggested I turn off the other DC power supplies in the rack, which I did.
  • Connected the new fuse blocks to the existing +24 V ones. Note that they are not contiguous but they follow the color code and will be labeled. 
  • I'm only using one of the new +24 outputs, but I made more for future use to minimize the number of times we have to turn the power off. 
• Connected the output of the amplifier to the EOM, and the coupled signal to the distribution box (which splits it and sends it to the demod boards). 
• Turned on the power switch and checked that the amplifier was in fact getting 24 V. 
• Connected the input from the 29.5 MHz source and measured the power coming from the amplifier. I measured -12 dBm instead of the expected ~0 dBm, but Gautam was able to see the expected power later, so maybe something just wasn't connected right.
• Double checked the power coming into the amplifier, which was consistent with earlier measurements at about 12.8 dBm. 

Still to be done:

• Label/relabel several things (fuse blocks, back panel, etc) 
• Current label on +24 Sorensen needs to be updated
• Order front panel and install
• Install power indicator lights on front and back 
• Readjust gains (analog and digital) to use full signal output and measure (hopefully) improved WFS performance
• Insert bi-directional coupler and measure modulation depth and reflections from EOM